The accumulation of ice on aircraft wings and other structural members in flight is a danger that is well known. As used herein, the term "structural members" is intended to refer to any aircraft surface susceptible to icing during flight, including wings, stabilizers, engine inlets, rotors, and so forth. Attempts have been made since the earliest days of flight to over come the problem of ice accumulation. While a variety of techniques have been proposed for removing ice from aircraft during flight, these techniques have had various drawbacks that have stimulated continued research activities. Efforts to prevent and/or remove such accumulations of ice has resulted in three generally universal approaches to remove accumulated ice, a process known as deicing.
One commonly employed method for deicing involves the application of a chemical to all or part of an aircraft to depress adhesion forces associated with ice accumulation upon the aircraft, or to depress the freezing point of water collecting upon the surfaces of the aircraft.
Another commonly employed method for deicing is typically termed mechanical deicing. In the principal commercial mechanical deicing means, pneumatic deicing, the leading edge zone or wing or strut component of an aircraft is covered with a plurality of expandable, generally tube-like structures, inflatable employing a pressurized fluid, typically air. Upon inflation, the tubular structures tend to expand substantially the leading edge profile of the wing or strut and crack ice accumulating thereon for dispersal into the air stream passing over the aircraft component. Other mechanical means for effecting deicing include electro mechanical hammering, such as that described in U.S. Pat. No. 3,549,964 to Levin et al., U.S. Pat. No. 4,690,353 to Haslim et al., U.S. Pat. No. 4,875,644 to Adams et al., and U.S. Pat. No. 4,706,911 to Brisco et al.
Another common approach for deicing is thermal deicing, wherein the portions of the aircraft that meet and break the air stream impinging on the aircraft are heated to prevent the formation of ice or to loosen accumulated ice. The loosened ice is blown from the structural members by the air stream passing over the aircraft.
In one form of thermal deicing, heating is accomplished by placing electro-thermal pads having heating elements over the leading edges of the aircraft, or by incorporating heating elements into the structural members of the aircraft. Electrical energy for each heating element is derived from a generating source driven by one or more of the aircraft engines. The electrical energy is intermittently or continuously supplied to provide heat sufficient to prevent the formation of ice or to loosen accumulating ice.
With some commonly employed thermal deicers, the heating elements are configured as ribbons i.e. interconnected conductive segments, that are mounted on a flexible backing. The conductive segments are separated from each other by gaps i.e. intersegmental gaps, and each ribbon is electrically energized by a pair of contact strips. When applied to a wing or other airfoil surface, the segments are arranged in strips or zones extending spanwise or cordwise of the aircraft wing or airfoil. In its simplest form an electro-thermal deicing pad consists of an electrical surface heating element sandwiched between two layers of insulation and attached or bonded to the surface or structure to be deiced. In operation, after a certain amount of ice has formed on the pad, the electrical current to the heater is turned on and when sufficient heat has been delivered to the pad/ice interfaced to destroy the adhesion between the ice and the pad thus permitting aerodynamic or centrifugal forces to remove the ice the heater has melted off.
Heretofore, flexible coverings of rubber or other elastomeric material have been used as outer skins for mechanical and thermal deicing systems. However, these rubber coverings when used on aircraft at higher speeds generally suffer objectional bowl abrasion, erosion, and cutting of the rubber by sand, rain drops, sleet and small ice particles impinging thereon. Prior electrically heated, flexible coverings of rubber or other elastomeric material with circular cross-section, solid or stranded wire, heating elements imbedded in the rubber of the covering may suffer breakage of the heating wires and also objectionable abrasion, erosion and cutting by rain drops and the like at high aircraft speeds.
It is an objective of the aircraft industry to increase the life time of such deicing apparatus. Efforts to improve such systems have led to continuing developments to improve their versatility, practicality, efficiency, and reliability.